In film productions, tokens are frequently used to indicate the start of new take or shot. These tokens may, inter alia, appear in the form of slates, often also referred to as clapperboards, clapboards or clappers. Other tokens can be vehicle license plates, traffic signs or posters. In a larger sense, tokens can be any objects having typical appearance and having readable symbols on it.
The term slate is used in the specification as a synonym of the term token.
In the following, the term slate is used interchangeably as a synonym of a token where appropriate for better understanding.
Slates typically have a body and a hinged arm, which is slapped against the body at the beginning of the take. Slates can additionally contain written, printed or electronically displayed information about the take. This information may include production title, scene title, take title, take number, date and time.
When producing a film, individual scenes are often taken repeatedly until the director is satisfied with the results or in order to have different views of the same scene for later selection. At the beginning of a take the slate is filmed and the slate arm is slapped to the slate body. The slapping of the slate may be used during post-processing for synchronizing the audio and video tracks. During a day of film production, a number of takes are captured, possibly by multiple cameras. Each camera will deliver one or more video sequences. Each video sequence—also called daily—contains a number of takes, up to several hundred. The video sequences may physically be contained on film rolls, magnetic tapes, hard disc drives (HDD), optical discs or other types of media. The format may be analog, digital, uncompressed or compressed, e.g. according to the MPEG standard. In general, accompanying audio tracks are captured with audio tools and stored on specific audio media.
After production, the dailies are post-processed. During post-processing the various takes are reviewed for quality and/or acceptability by the director and/or the cutter for identifying the take which will be used for the completed film. In order to find the beginning of a respective take, the video sequence is reviewed for the occurrence of slates. The correct and reliable identification of slates is important for several reasons. First, detected slates indicate the start of a new take. Second, extracted information from slates is necessary for shot processing. Third, identified slates assist in the synchronization of dailies with audio tracks. Audio-visual synchronization is realized either by using audio information from the slate or by detecting the time instant when the arm of the slate makes contact with the body. More recently introduced slates incorporate an electronic display, which continuously displays a time code. A time code control may then synchronize the time code in a sound recording apparatus and a camera. By doing so it is possible to assign to each image the accompanying sound information.
Until today, the process of searching slates in recorded material is often done manually, which is time consuming and sometimes cumbersome. Manual slate identification requires manually cueing or rewinding the recording to the occurrence of a slate, i.e. slate detection, and extracting the information on the slate. This task is performed by an operator using a video terminal with playback/forward/backward functions. The information from the slates is then read and manually entered into an audio-visual synchronization tool. After that, for synchronization purposes, the status of the slate arm has to be detected, i.e. the slapping of the arm to the body.
In view of the time consuming manual process of detecting the occurrence of a token in a video sequence, manually extracting the information on the token and entering the information into a synchronization tool, it is desirable to provide a method for automatically performing this task.